In recent years, infrared communication modules conforming to the IrDA (Infrared Data Association) standard have been rapidly scaled down in size, and the product of a short distance (20 cm) specification has its lens portion diameter and height reduced to about 1 mm to 2 mm. Concerning the communication speed, there is a gradual increase in speed with regard to IrDA, while compatibilities of a communication distance of several meters with high-speed characteristics of up to about 100 Mbps between a base station where a sufficient quantity of light is provided by arranging parallel twenty or more bullet type LED's and a terminal unit that has a sharp directivity and a tracking function are being established in optical wireless LAN products.
Such the wireless optical communication technique, which also has a problem of directivity and shielding, is expected to develop its applications as a high-speed interface of a palmtop or hand-held type portable terminal unit taking advantage of its high-speed characteristic, secrecy and particularly advantages in terms of cost. However, the high-speed optical wireless LAN (Local Area Network) products generally have a large size and considerably large power consumption. Moreover, there have been not a few attempts to use a comparatively inexpensive semiconductor laser of a near infrared wavelength region for wireless optical communications by making the semiconductor laser eye safe attaching importance to the high-speed performance in the past. However, there have been used comparatively large-scale diffusers and beam-shaping optical systems, and it has been difficult to achieve scaledown in size and low cost equivalent to those of the products conforming to IrDA.
That is, there has not yet been put to practical use a small-sized inexpensive optical communication module necessary for achieving a wireless optical communication system that buries the gap between the two of the existing IrDA and the optical wireless LAN and has a higher-speed wider-range communication area.